BSCI 424 — PATHOGENIC MICROBIOLOGY — Fall 2000

Enterococcus Summary

 

General Overview:

  Enterococcus faecalis and Enterococcus faecium: Most common, clinically relevant intestinal species

  Previously (1984) classified as Group D streptococci: Possess a Group D specific cell wall carbohydrate (glycerol teichoic acid linked to cytoplasmic membrane)

Morphology & Physiology:

  Nonmotile Gram-positive cocci in pairs or short chains (see WebLinked image): Difficult to distinguish from S. pneumoniae

  Catalase negative

  Most are facultative anaerobes

  Complex nutritional requirements (fastidious) (blood or serum required)

  Fermentative metabolism (carbohydrates to lactic acid)

  Halotolerant and bile resistant (adapted to niche in intestinal environment)

  Lancefield group D specific teichoic acid antigen

Clinical Syndromes:

  Important life-threatening nosocomial infections: Vancomycin Resistant Enterococci (VRE) are one of most important nosocomial pathogens of the 1990’s

  Urinary tract infections

   Bacteremia

  Subacute endocarditis

  Wound infections and intrabdominal abscesses are generally polymicrobial

  Foodborne disease

  Meningitis

Epidemiology:

  Inhabit the intestines of humans and animals

  Typically commensals: Capable of surviving in high concentrations of bile and sodium chloride

  E. faecalis colonize the large intestine (~10⁷ organisms per gram of feces) and urinary tract

  E. faecium colonize similar sites in lesser numbers

  Most infections originate from an intestinal site: Transmission also seen person-to-person and through consumption of contaminated food

  Risk factors for enterococcal infections:

 Urinary or intravascular catheterization

 Long-term hospitalization with broad-spectrum antibiotics

Pathogenesis & Immunity:

  Broad range multidrug antibiotic resistance: Mediated by R-plasmids that are "promiscuously" passaged between bacteria

  No single potent virulence factor: Colonization and secreted factors

 Fibrinolytic

 Protein and carbohydrate factors: Regulate adherence

 Bacteriocins: Inhibit competitive bacteria

Laboratory Identification:

  Large white colonies

  Typically nonhemolytic, but may be alpha- or beta-hemolytic

  Resemble S. pneumoniae in Gram stains

  Resist heat (60o C for 30 minutes)

  Most capable of growing:

  from 10^o to 45^oC range; optimal growth at 35^oC on nonselective agar (blood or chocolate agar)

  in 0.1% methylene blue milk

  in 40% bile salts (bile tolerant); colonies do not dissolve when exposed to bile (differentiates from S. pneumoniae)

  in 6.5% NaCl concentration (halotolerant)

  Readily distinguished from other a-hemolytic or g-hemolytic (nonhemolytic) Streptococcus spp. by:

  growth on Bile Esculin Agar (BEA) slants with blackening of the medium due to hydrolysis of esculin to esculetin

  production of acid from several sugars, including glucose, maltose and lactose

  growth in SF broth (Streptococcus [Enterococcus] faecalis broth) with production of acid

  resistance to optochin (differentiates from S. pneumoniae)

  Hydrolysis of pyrrolidonyl-beta-naphthylamide (PYR) (differentiates from S. pneumoniae)

Treatment, Prevention & Control:

  Antibiotic resistance makes treatment difficult

  Synergistic combination: Aminoglycoside and cell wall-active antibiotic (e.g., ampicillin, vancomycin)

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